DETERMINATION OF THE AGE OF METAMORPHISM OF THE JINSHA RIVER METAMORPHIC BEIT

The metamorphic rock series developed in the Jinsha River area on the Sichuan-Xizang（Tibet）border has long attracted the attention of the geological circle,and for years various schools have expressed different views on the age and nature of its metamorphism. In this paper,in the light of available geological data on the metamor- phism,magmatism and tectonic movements,the author proposes nine lines of evidence or indications and suggests that the present area experienced at least two phases of important metamorphic events:（i）the first phase took place in the late Hercynian time,starting at the end of the formation of the lower Permian E’aqin Group and terminating prior to the upper Permian deposition,and the metamorphism of this phase may be referred to as the late Hercynian high-pressure type regional metamorphism;（ii） the second phase took place in the period from the Triassic to pre-Pa- leogene,and the metamorphism may be called the Indosinian-Yanshanian regional dynamic metamorphism.The former is the main phase of metamor- phism,on which the latter was superimposed.